1. Field of the Invention
The present invention relates in general to a method and an apparatus for assembling a vehicle body, and more particularly to a method and an apparatus for assembling various types of vehicle bodies by using a flexible manufacturing system (FMS).
2. Description of the Prior Art
Hitherto, in order to assemble various types of vehicle bodies on a common assembling line, a so-called "flexible manufacturing system (FMS)" has been proposed and put into a practical use.
In such as assembling system, a method has been employed in which vehicle parts or work pieces (viz., main floor panels, body side panels, roof panels and the like) are temporarily positioned on a work piece carrier and then, the carrier is moved, together with the work pieces kept positioned thereon, to an assembling stage where the work pieces are to be spot-welded to constitute a desired structure for a vehicle body.
Such a method is disclosed in, for example, Japanese Patent First Provisional Publication No. 62-110581. That is, in the method of this publication, a plurality of program controlled positioning robots of orthogonal axes type are arranged on the work piece carrier, each robot being movable in the X, Y and Z directions of the rectangular coordinate system and having an arm which has at its leading end a work piece holder. In operation, given work pieces are held in position by the work piece holders of the robots on the carrier, and then the carrier is moved, by an external drive means, to an assembling position with the work pieces kept held in position by the work piece holders. At the assembling position, the work pieces are spot-welded by various welding robots.
Each time a changing of the type of the vehicle bodies to be assembled is required, a change is made to the control program for the robots to change the positions of the work piece holders thereon and to allow the work piece holders to appropriately hold the work pieces for the new vehicle bodies which are to be produced.
However, the above-mentioned method has the following drawback.
That is, because numerous robots are arranged on the carrier, the carrier is compelled to have numerous drive means (viz., servomotors) for actuating the robots. Thus, when it is intended to use a plurality of carriers of this type in the vehicle body assembling line, it becomes necessary to use a great number of servomotors and thus a great number of control units for controlling the servomotors. As is readily apparent, this results in a greater cost for the assembling line and a more complicated control system for the servomotors.